The present invention is directed to an assembly having a door situated with respect to a fixed structure, for preventing transmission of interference fields, especially high frequency electromagnetic fields. The door is disposed to be displaceable by hinge means with respect to the fixed structure, while the door and/or the fixed structure is provided with means, i.e. members for establishing contact between the door and the fixed structure to prevent transmission of interference fields.
The goal of structures used in order to produce a space that is shielded against interference, may be to prevent external electromagnetic energy from penetrating into the shielded space, or to confine electromagnetic energy to the space defined by the structure by preventing leakage of the field into the ambient surroundings. Structures of this type are known in the prior art, and are commonly employed to shield sensitive equipment against electromagnetic radiation, and to enable measurements which are free of radio-frequency interference, to be carried out in industry, research, and, for instance, by hospitals applying data transfer and high frequency technology.
Depending upon the intended use of the shielded space, the part of the shielding presenting poorest attenuation is usually the point of contact between the openable door, window, hatch or equivalent, which is indispensable for access to the shielded space and the fixed structure. In order to avoid effects impairing the shielding properties of the door, the electric contact between the moving part of the door and the frame, and the reluctance path in the case of shielding against low-frequency magnetic fields, should be as continuous as possible and should be equivalent to the properties of the rest of the structure. It is possible to improve the attenuation characteristics of the joint between the door and frame, above all when high frequencies are concerned, with a labyrinth structure disposed at the point of contact. Knife-like contact tongues on the door are pressed inbetween contact springs provided in a channel encircling the aperture, with the purpose of ensuring contact.
However, limitations have been imposed on the performance achieved in practice with door designs of the prior art, due to the fact that the particular use of a multiple labyrinth structure has not been possible because of requisite close fits, and at the same time preservation of normal convenience in use of the door and the operating characteristics of a closure hinged in a normal manner. When an efficient and complex labyrinth structure is used, the contact tongues entering between the springs, due to the close fits, tend to damage the seal structure by bending under the effect of the turning motion of a normally turning door, with the seal springs thus being pushed out of alignment. Moreover, closing of such a closure requires a very high pressing force, e.g. 300 to 400 kp.
U.S. Pat. No. 4,561,209 discloses a closure structure for preventing transmission of interference fields, where the movement of the door involves a swinging motion about an axis defined by hinge means and a substantially rectilinear movement producing contact which prevents transmission of interference fields. It has however been found that, in the case of certain large door designs, such swinging motion about an axis is not the best conceivable solution to the problem. In such cases, the great weight of the door imposes tremendous requirements on the hinge means. Therefore, the high force and moments acting on the turning hinge arrangements of the heavy door structure, cause greater stress on the hinge arrangement than in the case with lighter door structures.